Modification in Hcm Delay Model for Roundabout for Mixed Traffic Conditions - a Pilot Study

Khan, Asir; Dhamaniya, Ashish; Arkatkar, Shriniwas · 2022 · Crossref

DOI: 10.26552/com.c.2022.2.d92-d104

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Summary

This study addresses the challenge of evaluating roundabout performance in India, where traffic is characterized by high heterogeneity, lack of lane discipline, and diverse vehicle types. Existing guidelines, such as the Highway Capacity Manual (HCM) 2010, are designed for homogeneous, lane-based traffic and often fail to accurately reflect conditions in developing countries. The research aims to develop a methodology for modeling roundabouts under mixed traffic conditions using VISSIM microsimulation software, calibrate the model to reflect Indian driving behaviors, and determine modification factors for applying the HCM 2010 delay model to these heterogeneous conditions. The researchers selected three conventional four-legged roundabouts in Chandigarh and Jaipur, India, ensuring sites were free from external friction like parked vehicles or pedestrians. Data collection involved high-resolution video recording during peak and off-peak hours to capture turning movement counts, traffic composition, and vehicle trajectories. The study classified vehicles into two-wheelers, three-wheelers, small cars, big cars, light commercial vehicles, and buses. Critical gaps were estimated using Raff’s method for each vehicle type. The VISSIM 8.0 model was calibrated by adjusting conflict area settings, priority rules, and the Wiedemann 74 car-following parameters to replicate observed driver behavior, including lateral clearance and speed distributions. Validation was performed by comparing simulated and field data for travel times (microscopic validation) and critical gaps (macroscopic validation), using statistical t-tests to confirm model accuracy. The results demonstrated that the calibrated VISSIM model accurately replicated field conditions, with no statistically significant difference between simulated and observed travel times for various vehicle categories. The analysis revealed a negative exponential relationship between entry capacity and circulating flow. By comparing delay values derived from field trajectory data against those predicted by the HCM 2010 model, the study established Level of Service (LOS) thresholds specific to Indian conditions. The findings indicate that the standard HCM delay model requires modification to account for the unique interactions and gap acceptance behaviors in mixed traffic. The study successfully defined a methodology for determining these modification factors, allowing for more accurate performance evaluation of roundabouts in heterogeneous traffic environments. The significance of this work lies in its contribution to traffic engineering practices in developing nations. By providing a validated simulation methodology and specific modification factors for the HCM delay model, the study enables planners to design and evaluate roundabouts more effectively under mixed traffic conditions. This approach bridges the gap between Western-centric traffic models and the operational realities of Indian roads, offering a tool for improving safety and efficiency at unsignalized intersections. The pilot study establishes a framework that can be adopted for broader applications in similar heterogeneous traffic contexts.

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• intersection design